title: Ontogeny of the shell bones of embryos of Podocnemis unifilis (Troschel, 1848) (Testudines, Podocnemididae).
abstract: The aim of the present study was to investigate the sequence of shell bone formation in the embryos of the Pleurodira, Podocnemis unifilis. Their bones and cartilage were collected and cleared before staining. The shell was also examined by obtaining a series of histological slices. All the bony elements of the plastron have independent ossification centers, which subsequently join together and retain two fontanelles until the period of hatching. This turtle has a mesoplastra, which is characteristic of the Podocnemididae. The carapace begins to form concurrently with the ossification of the ribs at the beginning of stage 20. All the plates, except the suprapygal, initiate ossification during the embryonic period. The main purpose of the histological investigation was to highlight the relationship between the formation of the carapace and ribs with that of the neural plates. The costal and neural plates were found not to independent ossification centers, but to be closely related to components of the endoskeleton, originating as expansions of the perichondral collar of the ribs and the neural arches, respectively. Considering the ribs as an endoskeletal element of the carapace, the carapace and plastron begin ossification at the same stage in P. unifilis. This pattern reveals similarities with other Pleurodira, as well as evident variations, such as the presence of the seven neural bones and the presence of only one ossification center in the nuchal plate.
authors.affiliation: Comparative Anatomy Laboratory of the Federal University of Goiás-Jataí, 364 Km. 192, Jataí, GO, Brazil. fabianocl21@hotmail.com
authors.forename: Fabiano Campos
authors.initials: FC
authors.lastname: Lima
authors.forename: André Luiz Quagliatto
authors.initials: AL
authors.lastname: Santos
authors.forename: Lucélia Gonçalves
authors.initials: LG
authors.lastname: Vieira
authors.forename: Luiz Martins
authors.initials: LM
authors.lastname: Da Silva-Junior
authors.forename: Mariluce Ferreira
authors.initials: MF
authors.lastname: Romão
authors.forename: Simone Borges Salgueiro
authors.initials: SB
authors.lastname: De Simone
authors.forename: Líria Queiroz Luz
authors.initials: LQ
authors.lastname: Hirano
authors.forename: Juliana Macedo Magnino
authors.initials: JM
authors.lastname: Silva
authors.forename: Kennedy Mota
authors.initials: KM
authors.lastname: Montelo
authors.forename: Adriana
authors.initials: A
authors.lastname: Malvásio
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000196:embryology*; D002356:Cartilage / Q000196:embryology; D004625:Embryo, Nonmammalian / Q000033:anatomy & histology; D054258:Neural Plate / Q000196:embryology; D038081:Organogenesis; D010012:Osteogenesis; D012272:Ribs / Q000196:embryology; D014426:Turtles / Q000196:embryology*